A DC-DC converter is used extensively for a variety of equipments and apparatuses. However, in a given equipment or apparatus, there are a plurality of loads to which power from a power supply or power supplies is to be delivered. Moreover, load current value needed differs from one load to another.
For example, in a portable equipment, such as a digital still camera or camcorder, a load or loads in need of a heavier load current, such as an electric motor, and a load or loads in need of a lighter load current, such as a CCD (charge coupled device) or an LCD (liquid crystal device), exist together. For a heavier load, the frequency of a switching signal needs to be higher in order to get a load current that is needed. However, driving the light load with such high switching signal in turn increases switching loss. So, for a light load, it is beneficial to suppress the frequency of the switching signal to decrease the switching loss to improve the power supply efficiency.
Thus, a driving voltage outputting device, shown for example in Patent Document 1, includes a reference oscillator for each of multiple loads which is designed to generate a switching signal having a frequency appropriate for a load of interest. In this Patent Document 1, the reference oscillator is a triangular wave generator.
[Patent Document 1] JP Patent Kokai Publication No. JP-P2004-248377A